#@__ appeared in the sql statements

["who.cat" <win.acc@xxxxxxxxx>]

Studying a cms recently ,got a sql statement like this :
  Select * From `#@__homepageset`
i knew the '#@__' means the table prefix but how it like this ?
Did defined in the mysql  or in the php code .i could't find its definition
at present.Any phper's comments thanks in advance .

All you best
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